1. Field of the Invention
The present invention relates to a floating thin-film magnetic head and a composite type floating magnetic head for small hard disks in which a non-magnetic substrate is used as a slider.
2. Description of the Related Art
Floating magnetic heads which are for use in a small high-density 3.5-inch or 2.5-inch magnetic disk device are classified into two types: one, a thin-film magnetic head whose demand has been increasing in order to cope with a further increase in the recording density, shown in FIG. 1, and the other, a composite type magnetic head which has been currently used extensively, shown in FIG. 2.
FIG. 1 is a perspective view of an example of a thin-film magnetic head. A magnetic head 11 shown in FIG. 1 includes a slider 12, air bearings 13 and an electromagnetic converting unit 14.
In the electromagnetic converting unit 14, an Al.sub.2 O.sub.3 film is formed on an end surface of a non-magnetic slider, and a thin film, such as an amorphous film, is formed on that Al.sub.2 O.sub.3 film by the thin film lithographic process. Therefore, it is necessary to use proper materials so that the coefficients of thermal expansion of the materials may be in an appropriate relation to each other from the manufacturing and usage viewpoints, and a substrate material mainly composed of alumina-titanium carbide (ATC) is thus generally used as the slider material.
In the thin film magnetic head, the saturation magnetic flux density of the magnetic amorphous thin film is from 8000 to 9000 G, and the magnetic permeability thereof is about 2,000 (1 MHz). In order to achieve a high-density recording, a magnetic thin film of Fe--Al--Si exhibiting excellent soft magnetic characteristics has been put into practical use. The saturation magnetic flux density of the Fe--Al--Si thin film is about 11,000, and the magnetic permeability thereof is 3,000 (1 MGz). The coefficient of thermal expansion of the Fe--Al--Si magnetic thin film, which is (145.degree. to 150.degree.).times.10.sup.-7 /.degree.C., is larger than the coefficient of thermal expansion of the amorphous thin film, which is (120.degree. to 130.degree.).times.10.sup.-7 /.degree.C. Therefore, a non-magnetic substrate material in which Al.sub.2 O.sub.3 is added to the main components of MnO and NiO is used to form the slider in the thin-film magnetic head from the viewpoint of the coefficient of thermal expansion. The coefficient of thermal expansion of this non-magnetic substrate material is (135.degree. to 145.degree.).times.10.sup.-7 /.degree.C. Such a non-magnetic substrate has been proposed in, for example, Japanese Patent Laid-Open Publication Nos. 3-146456 and 2-296765, which substrate of this prior art has a rock salt structure of MnO, NiO, and is composed of 40 to 70 mol % of MnO and 30 to 60 mol % of NiO. Another non-magnetic substrate disclosed in Japanese Patent Laid-Open Publication No. 2-296765 has a rock salt structure of MnO, NiO, which is composed of 67 to 90 mol % of MnO and 10 to 33 mol % of NiO. These non-magnetic substrate materials have a desirable Vickers hardness from 550 to 700 kg/mm.sup.2, have less pores, can be readily precision machined, assure generation of less cracks and less chipping during machining, and are chemically stable.
FIG. 2 is a perspective view of a composite type floating magnetic head.
In FIG. 2, a composite type floating magnetic head 21 has a slider which is constituted by a non-magnetic substrate made of, for example, a ceramic. A magnetic head core 23 is fixed to and retained in a slit 25 formed in an air bearing 24 by a mold glass 26.
A Mn--Zn single crystal ferrite having a coefficient of thermal expansion of 120.degree..times.10.sup.-7 /.degree.C. at a temperature ranging from 100.degree. C. to 400.degree. C. is desirably used as the magnetic head core. If the coefficient of thermal expansion of the slider greatly differs from that of the magnetic head core, cracks are apt to occur in the glass which fixes the magnetic head core in the slit of the slider. Therefore, it is necessary that the coefficients of thermal expansion of both the magnetic head core and the slider are in levels approximating each other. One example of a non-magnetic substrate suitably used as such a composite type slider has been proposed in Japanese Patent Laid-Open Publication No. 2-243562. This non-magnetic substrate has a TiO.sub.2 --BaO--CaO type composition to which at least one substance selected from a group consisting of Al.sub.2 O.sub.3, NiO, SrO, MgO, Y.sub.2 O.sub.3, WO, MoO.sub.3, In.sub.2 O.sub.3 and ZrO.sub.2 is added. The coefficient of thermal expansion of this non-magnetic substrate, which is about 115.degree..times.10.sup.-7 /.degree.C., is close to that of the Mn--Zn ferrite. The crystal grains of this non-magnetic substrate are fine in size and uniform, and thus have less pores between crystal grains due to the addition of additives, such as Al.sub.2 O.sub.3. Therefore, the non-magnetic substrate has an excellent machining property and assures less occurrence of chipping.
In order to cope with a high-density recording which has been taking place in recent years, a hard disk in which a magnetic substance is closely attached to a disk substrate by plating or sputtering is used as a magnetic recording medium in the magnetic disk device.
Such a disk surface manufactured by plating or sputtering has a higher surface precision than a conventional coating type disk surface, and is coated with a lubricant. Due to this constitution, a sticking phenomenon, which would not be a serious problem in a conventional head, occurs between the head and the disk surface. More specifically, when the precision of the surface of the head which opposes the magnetic recording medium is high, the surface of the disk sticks to the surface of the head which opposes the disk when the disk is at a halt. A sticking force between the head and the disk may exceed the torque of a motor which rotates the disk. Such a sticking force makes the operation of the disk drive difficult and reduces the life of the head which performs the CSS (contact-start-and-stop) operation. Particularly, in a small magnetic disk which requires a floating height of 0.1 .mu.m or less, a sticking force causes a serious problem.
In order to alleviate the sticking phenomenon and thereby improve the CSS characteristics, it has been proposed to machine the surface of the head which opposes the disk so that it has a slight roughness.
For example, Japanese Patent Application No. sho 63-295652 discloses the floating magnetic head made of a polycrystal. In an air bearing surface of the above-mentioned magnetic head which opposes a magnetic recording medium, an average difference in the depth between the crests and the troughs is from 50 to 200 .ANG., an average pitch at which the crests and troughs are repeated is from 5 to 20 .mu.m, and an air bearing surface portion where a height defined as a difference between a crest and a trough changes very much is made to extend along the grain boundary of crystals. A monolithic magnetic head, which is an example of the above-described floating magnetic head, is shown in FIG. 8.
However, the monolithic type magnetic head is constituted by a soft magnetic substance of ferrite, and thus suffers from problems in that the inductance (L) of the material is large, in that the high-frequency response is poor, and in that noises are readily generated. Therefore, the monolithic type magnetic head is not suitable for use in a magnetic disk device whose recording density will be further increased in the future.
The maximum grain size of the non-magnetic substrate material, disclosed in Japanese Patent Laid-Open Publication No. 2-296765 and having a rock salt structure whose composition consists of 67 to 90 mol % of MnO and 10 to 33 mol % of NiO, is max. 1 .mu.m. The maximum grain size of the non-magnetic substrate material, disclosed in Japanese Patent Laid-Open Publication No. 3-146456 and having a rock salt structure whose composition consists of 40 to 70 mol % of MnO and 30 to 60 mol % of NiO, is from 3 to 4 .mu.m. Therefore, even when the surface of the non-magnetic substrate material is made irregular, it is impossible to obtain a desirable difference in the average depth between the crests and troughs and a desirable average pitch at which the crests and troughs are repeated, that is, it is difficult to improve CSS characteristics with these non-magnetic substrate materials in such a degree as the CSS characteristics are improved in the monolithic type magnetic head.
Various attempts have also been made in terms of the magnetic disk in order to improve CSS characteristics. The magnetic disk is subjected to a working called "texture". The texture is a working in which the surface of the disk substrate is made irregular in such a manner that it has an average surface roughness of about 10 nm and that crests and troughs are repeated at a pitch of 100 to 200 nn, as shown in FIGS. 9A and 9B by a roughness curve in the radius direction of a disk, measured by HIPOSS (a contact needle type fine form measuring device). After the texture, a base film of, for example, Cr is formed on the irregular surface of the disk substrate, and then a magnetic metal thin film of, for example, Co--Cr--Ta is formed on the base film by sputtering or the like. Subsequently, a protective film of, for example, carbon is formed on the magnetic metal thin film to manufacture a magnetic disk which is available on the market. The irregularities formed by the texture reduce the contact area of the disk with which the disk makes contact with the air bearing surface of the magnetic head, and thereby adjust the sticking force to an appropriate value.
In a composite type head for use in such a magnetic disk device, a non-magnetic substrate material in which at least one substance selected from a group consisting of Al.sub.2 O .sub.3, NiO, SrO, MgO, Y.sub.2 O.sub.3, WO, MoO.sub.3, In.sub.2 O.sub.3 and ZrO.sub.2 is added to a TiO.sub.2 --BaO--CaO type composition is suitably employed as a slider because of proper coefficient of thermal expansion and proper workability. However, this material having a Vickers hardness of about 850 kg/mm.sup.2 is so hard in hardness against the textured disk that there is such a problem as the crest portion of the disk is apt to be locally abraded by a magnetic head during a contact-start-stop period in which the magnetic head slides on the disk. Also, it is difficult to form a roughness on the surface of the non-magnetic substrate material, as in the case of a non-magnetic substrate material whose composition mainly consists of MnO and NiO and whose grain size is small.